1. Field of the Invention
The present invention relates to an apparatus for and a method of reducing the concentration of carbon monoxide and a fuel-cells generator system with such an apparatus. More specifically the present invention pertains to an apparatus for reducing the concentration of carbon monoxide included in a hydrogen-rich gas, which contains hydrogen and carbon monoxide and has a concentration of carbon monoxide lower than a concentration of hydrogen, and also to a method of the same. The present invention further pertains to a fuel-cells generator system with such an apparatus for reducing the concentration of carbon monoxide.
2. Description of the Related Art
In a fuel-cells generator system, supplies of hydrogen and oxygen are respectively fed to a fuel electrode and an oxidation electrode arranged across an electrolyte, and an electromotive force is generated through an electrochemical reaction on the electrodes. It is desirable to supply a hydrogen-rich gas to the fuel electrode, in order to enhance the power generation efficiency and prevents the air pollution.
A reformer is thus arranged before the fuel cells. The reformer reforms a crude gaseous fuel, which includes a hydrocarbon, such as methanol, or an alcohol as the primary component, to a hydrogen-rich gas in the presence of a reforming catalyst. Even in the reformer of enhanced ability, however, contamination of the reformed gas with a small amount of carbon monoxide is inevitable. Existence of carbon monoxide in the reformed gas fed to the fuel electrode poisons platinum (Pt) carried as a catalyst on the fuel electrode, thereby lowering or unstabilizing the performance of power generation.
A technique proposed for preventing such a phenomenon selectively oxidizes carbon monoxide included in the reformed gas in the presence of a catalyst, thus reducing the concentration of carbon monoxide included in the gaseous fuel fed to the fuel electrode.
As disclosed in JAPANESE PATENT LAYING-OPEN GAZETTE No. 7-185303, another proposed technique uses a cooling layer arranged in a catalyst layer with the catalyst packed therein, thereby preventing the temperature of the catalyst from exceeding an active temperature range. This technique enables the catalyst to be kept in the active temperature range and accordingly reduces the concentration of carbon monoxide to a level that does not poison the catalyst on the electrodes in the fuel cells.
In the proposed technique, a coolant flowing through the cooling layer is a liquid mixture of water and methanol, which is the reforming material. This may cause part of the coolant to be vaporized in the cooling layer. Vaporization of the coolant raises the pressure in the cooling layer and prevents the coolant from flowing at a constant flow rate. The pulsative flow of the coolant causes non-uniformity of temperature in the cooling layer and thus prevents the whole catalyst layer from being cooled homogeneously. As a result, all the catalysts packed in the catalyst layer can not be kept within the active temperature range.